1. Field of the Invention
The present invention relates to thickening apparatus, paper making machines and the like, used in the paper making industry and more particularly, to a cylinder mold for use in a thickening apparatus.
2. Prior Art
In the paper making industry, a device commonly referred to as a thickener or decker basically comprises a vat with a controlled infeed and a discharge outlet, and a cylinder mold, namely a cylindrical porous shell, is suspended for rotation in the vat and with the hollow central portion of the shell in communication with a white water discharge outlet. As the cylinder mold is rotated, the fibers in the pulp slurry adhere to the porous surface of the cylinder mold and water is discharged through the mold into the hollow center from where it is subsequently removed, depositing a dewatered fibrous web on the outer surface of the mold. A couch roll in contact with the surface of the cylinder mold then removes the fibrous web in a well known manner for its subsequent processing into paper.
The cylinder mold, which plays a very important part in the thickener apparatus, is usally constructed with a long solid steel center shaft with a plurality of spaced, spoked support members upon which a spirally wound wire or screen mesh is supported, to form the outer surface of the cylinder mold. Cylinder molds constructed in this manner are very expensive and relatively heavy because of the large central shaft utilized to support the mold. A major difficulty associated with such prior art devices is that since the outer porous shell is relatively flexible and thin, it is often deformed during use because the heavy central shaft causes the shell to deflect more than it normally would due to its own weight, since the heavy shaft will deflect more than the shell.
Attempts have been made to overcome this difficulty be development of shaftless cylinder molds of a variety of constructions. Such constructions are disclosed, for example, in U.S. Pat. Nos. 3,091,563, 3,577,315, and 3,773,614. These devices use a variety of forms to support the shell and give the cylinder mold the necessary rigidity to remain substantially cylindrical during use.